Many biochemical processes are mediated by multisubunit protein-DNA complexes. We are interested in understanding structure-function relationships in the assembly and activity of such complexes, particularly those that catalyze genetic recombination. Many recombinases are amenable to such studies as they function in complexes whose components are well defined and readily characterized. This study will focus on the S. cerevisiae protein Flp, which is a member of the 1 integrase family of recombinases. In addition to their importance in microbial survival, these enzymes, particularly Flp and its distant relative cre, are extremely useful tools for genetic manipulation. This project will use a combination of crystallographic and biochemical experiments to study the structure and assembly of recombinogenic Flp- DNA complexes. The immediate goals are to obtain the structure of Flp complexed with substrates that mimic different points along the reaction pathway, and to complement this data with protease accessibility experiments probing the conformation of the protein under different contexts in solution. The domain structure of the protein and the possibility of small peptide inhibitors will also be investigated. The latter will both test our understanding of complex assembly and serve as useful biotechnology tools. The long-term goals of this work are a better understanding of the strategies used by recombinases to rearrange genetic material, and of the strategies used to link enzymatic function to proper complex activity. These studies will also provide a database for future protein engineering studies to improve the usefulness of Flp as a genetic tool.